Printed circuit board

Abstract

The present invention provides a printed circuit board in which electrode layers can electrically be connected by an inner-through-hole connection, the coefficient of thermal expansion of the board is equal to that of a semiconductor, high thermal conductivity can be obtained and wiring can be formed at a high density. A cover film is laminated on both surfaces of a resin impregnated fabric sheet, holes are formed by laser beams in the direction of the thickness of the sheet and cover film, an electrically conductive paste that contains the electrically conductive particles and a thermosetting resin is filled in the holes. The cover film is removed, a copper foil is placed on both sides of the sheet, and pressed and heated, and the resin component of the sheet and that of the electrically conductive paste are hardened. The copper foil is etched to form circuit patterns, and further etching removes the electrically conductive particles present at a surface layer portion so that an electrical insulating layer is thus formed.

What is claimed is: 
     
       1. A method for manufacturing a circuit board, comprising the steps of: A. laminating first and second cover films onto opposed surfaces of a resin impregnated fabric sheet,   B. forming a plurality of through holes in the direction of the thickness of the sheet and first and second cover films,   C. filling the through holes with an electrically conductive paste that contains electrically conductive particles and a thermosetting resin,   D. removing the first and second cover films,   E. placing a metallic foil on the opposed surfaces of the sheet, pressing and heating the sheet, and hardening the resin impregnated in the fabric sheet and the thermosetting resin in the electrically conductive paste, and   F. etching the metallic foil, thereby removing a portion of the foil that blocks a first group of the through holes, forming the metallic foil into a predetermined circuit pattern, further etching to remove the electrically conductive particles present at a surface layer portion of the first group of through holes, thereby forming an electrically insulative layer having a surface layer portion formed of the thermosetting resin.   
     
     
       2. A method for manufacturing a printed circuit board, comprising the steps of: A. laminating first and second cover films onto opposed surfaces of a resin impregnated fabric sheet,   B. forming first and second through holes in the direction of the thickness of the sheet and first and second cover films,   C. filling the first through holes with an electrically conductive paste that contains electrically conductive particles and a thermosetting resin and filling the second through holes with an electrically insulative paste that contains thermally conductive, electrically insulative particles and a thermosetting resin,   D. removing the first and second cover films,   E. placing a metallic foil on the opposed surfaces of the sheet, pressing and heating the sheet, and hardening the resin impregnated in the fabric sheet, the thermosetting resin in the electrically conductive paste, and the thermosetting resin in the electrically insulative paste, and   F. etching the metallic foil, thereby removing a portion of the foil that blocks the second through hole and forming the metallic foil into a predetermined circuit pattern.   
     
     
       3. A method for manufacturing a printed circuit board, comprising the steps of: A. laminating first and second cover films onto opposed surfaces of a resin impregnated fabric sheet,   B. forming first, second and third through holes in the direction of the thickness of the sheet and cover films,   C. filling the first and second through holes with an electrically conductive paste that contains electrically conductive particles and a thermosetting resin and filling the third through holes with an electrically insulative paste that contains thermally conductive, electrically insulative particles and a thermosetting resin,   D. removing the first and second cover films,   E. placing a metallic foil on the opposed surfaces of the sheet, pressing and heating the sheet, and hardening the resin impregnated in the fabric sheet, the thermosetting resin in the electrically conductive paste, and the thermosetting resin in the electrically insulative paste, and   F. etching the metallic foil, thereby removing portions of the foil that block the second and third through holes, forming the metallic foil into a predetermined circuit pattern, further etching to remove the electrically conductive particles present at a surface layer portion of the second through hole, thereby forming an electrically insulating layer comprised of the thermosetting resin on the second through hole.   
     
     
       4. The method for manufacturing a printed circuit board according to claim 1, wherein the electrically conductive particles are selected from the group consisting of Au, Ag, Cu, Al, Pd, Ni and alloys thereof. 
     
     
       5. The method for manufacturing a printed circuit board according to claim 2, wherein the thermally conductive insulating particles are at least one of alumina particles, silica particles and magnesia particles. 
     
     
       6. The method for manufacturing a printed circuit board according to claim 1, wherein the resin impregnated in the fabric sheet and the resin in the electrically conductive paste are thermosetting resins. 
     
     
       7. The method for manufacturing a printed circuit board according to claim 6, wherein the thermosetting resin is an epoxy resin. 
     
     
       8. The method for manufacturing a printed circuit board according to claim 1, wherein a metallic foil pattern having a portion that is bonded to an electrically conductive paste is formed on at least one of the opposed surfaces of the resin impregnated fabric sheet. 
     
     
       9. The method for manufacturing a printed circuit board according to claim 1, wherein the sheet is a nonwoven fabric of a heat resistant synthetic fiber or a paper impregnated with a thermosetting resin. 
     
     
       10. The method for manufacturing a printed circuit board according to claim 9, wherein the sheet is formed from a heat resistant synthetic fiber that is at least one of an aromatic polyamide fiber and a polyimide fiber.